The invention is applicable in all areas of industrial measurements technology, as well as medicine and laboratory technology, in which liquids are transported, dosed or metered in controlled form, especially with the assistance of microfluidic systems or in the field of micro-methods technology. This is especially the case in the field of analysis of liquids. Examples of this include analytical systems for monitoring and optimizing the cleaning effectiveness of clarification plants, for drinking water monitoring, for monitoring biotechnological processes or for quality monitoring of industrially applied liquids or food. Measured and monitored are, for example, the content in liquid samples of substances, such as e.g. ions, for instance ammonium, phosphate or nitrate, biological or biochemical compounds, such as e.g. hormones, or microorganisms, e.g. bacteria.
In such systems, besides the liquid to be analyzed, also, in given cases, additional liquids required for their analysis, such as e.g. reagent solutions, must be dosed, or metered, in predetermined amounts, and, in given cases, certain desired volumes of different liquids must be mixed, and/or certain desired volume flow rates of liquids through lines or measuring- and/or analytical units must be produced.
In order, especially in the field of analysis, to be able to achieve an as high as possible measure of automation, apparatuses and methods are required, by which the, in miniaturized systems required, as a rule, very small desired volumes of less than 50 mL, especially less than 10 mL can be dosed, and by which small volume flow rates of less than 5000 μL/min, especially less than 1000 μL/min, of the liquids through the individual systems can be controlled as a function of the predetermined volume flow rates desired, in each case, for the process or method to be performed.
For the transport of these liquids, today, for example, peristaltic pumps are applied. Peristaltic pumps bring about, however, due to their functional principle, as a rule, pulsating volume flow rates. Additionally, the elastic hoses used in connection with peristaltic pumps are subject to aging, which affects the transport power of peristaltic pumps. In these ways, the accuracy, with which certain desired volumes of a liquid can be filled, or desired predetermined volume flow rates can be provided, is limited.
Another frequently applied variant for the transport of the liquids is syringe pumps. These are distinguished by high accuracy and uniform flow characteristics. However, standing against the application of syringe pumps in automated systems is their high price and their low robustness.
Volume flow rates can be achieved simply by pneumatic apparatuses, in the case of which liquid flows as a result of pressure loading of the liquid in a supply container with a gas, especially with air. Typically, however, the flow resistance of these systems changes with time, due, for instance, to the increasing emptying of the supply container, so that, in this case, a control of the volume flow through the system is required.
For this, the volume flow rate can be measured e.g. by corresponding flow sensors integrated in the liquid system. Such flow sensors are described, for example, in WO 2007/147786 A1. These sensors are, however, expensive and come in direct contact with the liquid. The latter feature introduces the danger of fouling both of the sensor as well as also the liquid.